1. Field of the Invention
The invention relates to a control device and control method for an internal combustion engine, which execute feedback control such that the rate of decrease in engine rotational speed coincides with a target rate of decrease.
2. Description of Related Art
There is known control over an internal combustion engine, in which, when accelerator operation is released, feedback control that executes feedback control over the rate of decrease in engine rotational speed so as to coincide with a target rate of decrease to thereby stabilize the behavior of a variation in engine rotational speed at the time when the engine rotational speed decreases with the release of accelerator operation.
In order to appropriately execute feedback control over the rate of decrease in engine rotational speed so as to coincide with the target rate of decrease, it is necessary to appropriately control the torque of the internal combustion engine on the basis of a deviation from the target rate of decrease. For this purpose, a feedback gain needs to be set at an appropriate value.
In contrast to this, Japanese Patent Application Publication No. 2000-073801 (JP 2000-073801 A) describes a control device for an internal combustion engine. When the engine rotational speed is likely to decrease, the control device increases the feedback gain as compared with when the engine rotational speed is not likely to decrease to thereby suppress a decrease in engine rotational speed.
The invention described in JP 2000-073801 A is to execute feedback control so as to coincide the engine rotational speed itself with a target engine rotational speed. Such a configuration that the feedback gain is increased when the engine rotational speed is likely to decrease as compared with when the engine rotational speed is not likely to decrease may be applied to feedback control.
Incidentally, the rate of decrease in engine rotational speed varies with an external load that acts on the output shaft of the internal combustion engine, so, even when the above configuration described in JP 2000-073801 A is applied to feedback control, an appropriate feedback gain cannot be set when an external load varies. Thus, it may be difficult to appropriately suppress a deviation of the rate of decrease.
Note that such a problem not only exists in feedback control during a period from when accelerator operation is released to when the engine rotational speed reaches an idle rotational speed but also it commonly exists in overall feedback control that executes feedback control over the torque of the internal combustion engine so as to coincide the rate of decrease in engine rotational speed with a target rate of decrease in the engine rotational speed.